Composition for insulating wire



May 31, 1938. E. H. CONVERSE COMPOSITION FTOR INSULATING WIRE Original Filed Jan. 3, 193.71

Nm, ha wm, *y MN m( l LIN) d. n

lNvENToR ateluteel May 31, 1938 NITE STATES PATE signor to James K.

N. Y. l

Delano, village of Rye,4

l Original application `lanuary 3, 1933, Serial No.

Divided and this application February 12, 1935, Serial No. 6,147

8 Claims.

This invention relates to a composition and process for electrically insulating wire so that the wire will be provided with a coating which will have desirable mechanical characteristics in addition to being non-inflammable and of high dielectric strength. Certain features of this application were disclosed in my prior applicanon, ser. sie. 516,833, sied February 1s, 1931. This is a division of my application, Ser. No. 649,740, flled January 3, 1933, now Patent Number 2,059,441.

A feature of the composition is that it forms a coating that is impervious to softening or dis solving in either mineral or vegetable oils.

A further feature is that wire may be insulated by this process at a far greater speed of produc tion than the varnish type of enamel coatings, and in such a manner as to provide a coating solution' from which there is no loss of solid content in process due to exposure, air or heat. However, the thinner or solvent that is used may be recovered.v A substantial saving over the varnish type of coating is effected with this invention, while all of the mechanical and electrical advantages of the varnish type of coating are retained and on several points of comparison bettered.

`Many attempts have been made heretofore to use the esters of cellulose for coating wire for insulating purposes, with results, when compared to the varnish type as at present in use, that have prevented the cellulose coating from taking its place in the enameledv wire field.

Heretofore when either the acetate or the nitrate ester of cellulose was used and applied to Wire as a varnish, the coatings have had extremely poor adhesion to the metal wire, were not flexible enough, became brittle on agei'ng, would not stand the stretch test without cracking or tubing and were in general not a product which would compete with the varnish type of coating. By the varnish type I mean the prevalent tung oil, resins, linseed oil, etc., type which is baked or polymerized by heat upon the wire or conductor. The test specifications for this varnished Wire are extremely rigid and have heretofore not been met by the cellulose types of coating, either applied as a varnish with suitable solvents or mixed with phenol or reaction types of mixtures or mixed with synthetic resins and plasticizers, etc.

It has been found that reaction types of mixtures used as coatings, while giving adhesion, also give brittleness and tube readily on stretching the wire and the insulation cracks or checks on a sharp bend test, but the greatest drawback is in the manufacturing process, as usually theA (Cl. 10G-15) of the acid or alkali type, gives a poor insulating coat as its presence apparently leaves the coating hygroscopic.

Plasticizers used in such coatings usually, while lending flexibility, give poor adhesion and gradually dry out, thereby causing brittleness. Natural resins as used heretofore usually cause the coating to soften when heated to the extent that usually occurs in the average electrical appliances which use this type of wire. These resins are detrimental, as they cause short circuits to occur between turns of a coil, etc. They-also cause brittleness, etc. when they are baked on the wire at a heat sufcient to overcome the softening effect above described.

I find that-cellulose acetate can be utilized in making varnish coatings without sacriiice of any of the important characteristics, electrical or mechanical, by the process herein described. These coatings are very desirable as they have further advantages of their own.

Commercial cellulose acetate in its raw state,

resembles dry white asbestos somewhat. If this dry material is heated in a ladle over a Bunsen flame carefully it Will go to a semi-fluid mass resembling melted sugar in appearance. When the melted'mass cools it forms a solid translucent cake that is brittle and non-elastic and has no marked adhesive qualities.

' Commercial furfural (C4'.H3IO.CHO)fis a high temperature boiling liquid solvent for cellulose acetate. It has the property of forming inherent resins in its liquid body. 'Ihat is, even if furfural is distilled until it is water-white it will gradually go back to its normal color, a very dark brown, almost black, due to inherent resinication, the resinli'lcation slowing' up when it approaches a given point of saturation. The furfural resin is always present in the regular grade of commercial iurfural. i

Upon evaporatng commercial furfural, a tarry resin residue remains. If this tarry residue is mixed with dry cellulose acetate and stirred in when the acetate is in a heated uid condition, a mass is obtained on cooling which' is of a horny character. It is a somewhat elastic extremely tough cake of high gloss that has great adhesive strength, and is hard to get out of the ladle. Tests show high dielectric strength. It is this composition which I use for my insulating coating.

It is to be noted that the` resin cellulose mix' ture will melt at a lower temperature than when cellulose alone was heated, showing that the resin probably exerted a solvent action upon the cellulose under heat.

In my process, I do not distill oil the liquid n from the coating fllm leaves the resin ,residue perfectly combined with the cellulose coating.

For example, I dissolve cellulose acetate in a low boiling solvent, in a mixture such as acetone, or methyl or ethyl acetate or ethylene dichloride and alcohol or a solvent withv diluents, such as benzene with methyl or ethyl alcohol, and to this I add 30% of commercial furfural using '70% of the low boiling solvents and use sufiicient acetate to make up a to 20% solid content solution. It is to be noted that the.. acetate.v can be, had in various viscosities and ifa lowy viscosity is used a high solid body content can be had without sacrifice of fiowability and covering qualities for coating the wire.

The proportions may be varied from those given, but less than furfural does not give good results. I may also use furfural alone without other solvents, but this would require increasing the time of drying the coating which is important from the high ratev production standpoint which my process has in its; favor.

The coating solution made from the above ingredients will not change its form or viscosity and will keep indefinitely in storage and in process as against the reaction resin types of cellulose coating solutions which continue to react in storage and during the process of applying them.

In order to use this coatingv to its full advatage I employ an oven having distinct increasing heated zones. By this I mean portions of the heat where the freshly coated wire enters, a portion where the low boiling solvents such as the acetone, leaves the coating, a portion where the high boiling furfural leaves the film, and a portion of the oven where the dry wire is exposed to high heat to cause the resin residue and cellulose to effect a combination together on the wire to give the proper finished coating.

The length of oven having the heat arranged as described will determine the speed at which the wire can be coated, an oven 8 feet long having two distinct compartments, upper and lower, arranged for the wire to enter and return through each compartment, will give a production rate eight times that of similar size wire when the varnish process is used.

The upper compartment has a room/temperature of, say, 70 degrees F. to 2,50 degrees F., and the wire will come out of this compartment dry in all respects. It goes around a sheave wheel and is returned through the lower compartment at a graduated temperature of, say, 250 to 500 degrees F.

'I'he steps the coating takes in driving in the oven, etc., are very important so I stress the point that for various low boiling solvent mixtures the oven drying temperatures must be adjusted to them to make perfect wire, as various solvents have diiferent evaporating rates and the heat in.

the ogen should be adjusted to suit these while the wire travels at a certain speed, the speed being determined largely by the size of the wire.

As an example, I may use 70% acetone and furfural by volumeand enough cellulose to make up a. 15% solid body solution. I employ only enough heat in the first portion of the oven to cause the acetone to-leave the wet coating without disruptive action. It does this between the room temperature at the oven entrance and about 150 degrees F. point of heat in the oven, so my heated portion of the oven for this solvent is made long enough to allow time for the acetone to leave the coating; the furfural begins to go oiI at this temperature, but enough remains to keep the film of coating semi-liquid so that the vapors of the acetone can leave without causing pinholes. That is, if they do bubble'through, the coating will again seal. The furfural has a higher boiling point (166 degrees C.) and gradually goes off as vapor when the wire coating goes into the 200 degrees F. zone of the oven. It has left the film when it reaches the 250 degrees F. zone, so that the coating is then dry on the wire. The wire can then be handled, run over pulleys, etc., without damage or injury to the coating, vbut if spooled for use at this stage it would show the same mechanical defects, i. e., poor adhesion, tubing under stretch test, brittleness when aged by standing, only fair dielectric strength, etc., as is the case with prior attempts at a cellulose type of coating for wire insulation. After this treatment I pass the wire into the highest heat zone of the oven where the residue resin that was formerly in the liquid furfural is dispersed throughout. The cellulose is heated and an apparently new combination or reaction under the heat is effected, which greatly changes the characteristics of the coating as it now adheres firmly to the wire. It will stretch without tubing to the extreme breaking point of the Wire; it will not soften with heat; it is of high dielectric strength; it is not hygroscopic; it stands boiling oils both vegetable and mineral; it does not become brittle even when exposed to oxygen gas for what with the amount of furfural residue and the however, is to soften the coating in the high heat on the wire. I do not mean by saying that the coating is softened that it becomes fluid, but it becomes plastic and when once cooled of! will not soften again under heat, but will char rather than become soft, so I conclude that the cellulose has changed its chemical form and properties in some manner.

The low boiling solvents which I use maybe recovered by connecting the low heat portion of the oven to av proper solvent recovery system. This is not possible with the varnish type of coating as the high heat used for baking (600 to 900 degrees F.) causes the resins and oils to distil and throw ofl' a. smoke which is gummy and cannot be so recovered. Also, the varnish will iel and a skinwlll form. over it where it is exposed cient solvent to give it proper fluidity as the solid content will readily redissolve again, as no reaction materials are employed, nor does it oxidize if exposed to air.

-I have substituted cellulose nitrate for the acetate and which the proper heat which is more.

critical in the higher stage and found the same advantages, but the nitrate coated wire is not reproof andno apparent advantage is gained byr practical irom a production standpoint. Since the solution employed is capable of high speed working, a proper oven with the stages of heat as described above gives the better results.

l The accompanying drawing shows the temperature of these heat stages where the low boilingA solvent is acetone, the oven being eight feet long with the rate of wire travel 400 feet per minute.

Only one coating is shown for the sake of clearness and in practice three to ve coats are generally employed depending on the thickness of the insulation required.

Where thevwire is of considerable mass and going through the process at high speed, the heat can be somewhat higher as the wire is not in step or is lagging behind the oven temperatures so the heat must be adjusted accordingly. e

There may be other chemical bodies ci high boiling 'qualities which could be used in place of furi'ural and I wish to point out that I could add the furfural residue resin separately to the cellup lose and I wish to include such within the ap'- pended claims. It is also possible to mix in other high boiling solvents with the iurfural, such as ethyl lactate, diacetone alcohol, dichlorethy'l ether, ethyl glycol acetate alcohol in proper proportion using them for their high boiling qualities, ii required, without departing from the resuits obtained, where heat treatment as described would impart to the coating the desired properties. 50

The drawing shows a partial longitudinal section of a somewhat diagrammatic layout of apparatus suitable for carrying out my process.

The numeral I denotes a horizontal oven divided into an upper chamber I I and a lower chamber I2, while below the lower chamber I2 is y mounted a guard I 3 forming a burner chamber Il within which is mounted any suitable heating element such as a gas burner I5 which is fed from the gas pipe I6; said burner being formed with a series of holes for escape of the burning gas.

T'he guard I 3 is formed with a series of holes 3l for supplying air to the burner, and the bottom of the lower oven chamber I2 is also formed with a series of holes 32.

Adjacent one end oi the oven is mounted the coating applicator I1 which is suppliedwith coating solution from thesupply tank I8, the wire I9 traveling through the applicator I'I, where it receives its coat. from the sheave 24 and supply spool 26, through the upper chamber I I, around the sheave 23 and back through the lower chamber I2, over the shea've 25 to the take-up 4'spool 2li which is rotated by a source of power III.

The chambers II and I2 areeach provided with the ends 32 having an opening through which the wire can, pass, and also with the dividing lwalls 2@ which are also provided with openings' for the wire and which divide the oven` chambers into zones of dierent temperatures as indicated, and vents 25 are arranged so that heat will pass up into the upper chamber from the lower to maintain the temperature correctly in the dierent portions or zones, and these vents are provided with adjustable closures 26.

If the circulation of air is arranged lcorrectly the dividing walls 29 may be dispensed with as the draft up the stack 22 will pull the heat to the stack end of the oven, thus the heat will be higher at thestaclr end of the oven. f'

The lower oven chamber I2 is provided with a vent stack 22, lwhich may also communicate with the upper chamber II, and the other end of the upper chamber II is provided or connected with a solvent recovery apparatus having a sucber II.

It is understood that any other suitable con struction and arrangement may be used in place of that shown or indicated.

The oven could have` a single compartment if desired, the wire entering at one end and'leaving at the other end, or could be arranged vertically instead of horizontally and is adaptable to various'requirements so lorig as different heats are formed for drying and iinal heating of the coating.` y

I claim:

' l. A new composition of matter consisting substantially entirely oi cellulose ester and furfural residue resin heated together to a thermoplastic state.

2. A new composition of matter consisting substantially entirely of a cellulose ester' and furi'ural heated together to the softening point of the ester.

3. A new composition of matter consisting substantially entirely of cellulose acetate and commercial furfural having inherent resin therein heated together to the point of partial concurrent melting oi the acetate and the resin.

4. 'A new composition of matter consisting substantially entirely of cellulose acetate and com- .mercial furfural having inherent resin therein heated together to a temperature which causes lthe mixture to fuse.

5. Insulating material consisting substantially entirely of a cellulose ester and resinified furfural.

6. Insulating material consisting substantially entirelyof a. cellulose ester and resiniiied furfural and heated sufficiently to obliterate pinholes.

7. A new composition oi matter consisting substantially entirely of cellulose acetate and furfural residue resin heated together lto a thermoplastic state.

8. Insulating material consisting substantially entirely of a cellulose acetate and resinified i'ure fural. Y

EDWARD H. CONVERSE. 

